Superchargers are devices that include an air pump or blower wheel, rotation of which changes the pressure conditions in the inlet system of the engine, the inlet pressure. Commonly the device is configured and operated in a way that increases the inlet pressure and therefore enables the power output of the engine to be increased. Alternatively the device may be configured to lower the Inlet Pressure and reduce the power output, this method of power control offering efficiency advantages when compared with the conventional method of load control through a throttle valve.
An air blower in accordance with the invention may, however, also take other forms, such as an automotive cooling fan for blowing air over a cooling radiator.
Currently Superchargers are driven mechanically (usually with fixed speed ratio) by the engine, electrically or by a turbine which extracts energy from exhaust gases (known as Turbochargers).
With practical applications the simple mechanical drive has certain disadvantages including insufficient ability to increase performance at low engine speed and poor power control capability. At high engine speed and load, wasteful bypass or dump valves are sometimes required to prevent inlet pressure becoming higher than required or desired.
Practical applications of electrically driven superchargers are often limited by the cost, mass and package size of the electrical machinery required to power the supercharger when high power output is required from the engine. The efficiency of these devices is also compromised by losses incurred when converting mechanical energy into electrical energy and vice-versa.
Practical applications of Turbochargers are commonplace. The inlet pressure available at a given condition is very strongly dependent on the exhaust gas flow rate, temperature and pressure however. Under transient conditions when the rotational speed of the device changes, the inertia of the rotating components also substantially affects the inlet pressure. These effects often result in an undesirable lack of power output from the engine at low engine speed and under transition from low power output to high power output. These characteristics are particularly undesirable in automotive applications. Consequently various attempts have been made to improve the performance of Turbochargers in these respects. Some improvement is enabled by providing guide vanes with variable pitch. This technology is commonly applied to automotive diesel engines but benefits to gasoline engines are limited by higher exhaust gas temperature and associated materials technology and lubrication issues.
Previously it has been proposed that a supercharger can be mechanically driven by the engine via a transmission system with a continuously variable speed ratio. This offers large improvements in performance at low engine speed and in load control. For reasons which include cost, reliability, durability and package size, systems of this type have generally proved to be unattractive to the market.
It is therefore the object of the invention to provide a supercharger which is commercially attractive, efficient and which is able to vary inlet pressure across a wide range independent of engine speed.